Injection molding provides a convenient way for preparing various articles from thermoplastic resins, particularly objects of a relatively intricate nature. In order to injection mold articles in an economic manner, it is important to minimize the adhesion of the molded part to the mold surface through the use of a release agent. It is additionally advantageous that the release agent be incorporated in the material to be demolded. However, such an internal agent must be compatible with the resin as measured by the usual characteristics of the resin under normal conditions and heat treatments.
Of the thermoplastic resins which find a mold release agent useful from time to time one of the most sensitive to chemical attack or degradation is polycarbonate. The carbonate bond is susceptible to bond cleavage, for example, hydrolysis from the usual sources. Acids and various acid derivatives have been used as mold release agents for polycarbonate. Examples of carboxylic acids employed as mold release agents for polycarbonate include U.S. Pat. Nos. 4,409,351 and 4,408,000. Examples of carboxylic acid esters useful as mold release agents for polycarbonate include U.S. Pat. Nos. 3,836,499; 4,097,435; 3,784,595; 4,065,436; 4,131,575; 4,444,935; and 4,446,268. Amides in general are also known as additives useful in improving the processing of polycarbonates, U.S. Pat. No. 4,119,603. Certain carboxylic acid amides have been employed as mold release agents in polycarbonate but have met with limited utility. Specifically, the Mitsubishi Gas Chemical Japanese application No. 72 41092 describes three different amides--lauryl amide, stearyl amide and ethylene bis stearamide-- as mold release agents for polycarbonate at 0.5 wt. percent levels and found that an ester exchange reaction with the polycarbonate had occured. It has also been found that amides lead to unacceptable drops in melt viscosity.
It is thus perceived that amides would not be thought to be useful additives for polycarbonate. It has now been surprisingly found that a limited class of amides are effective mold release agents for polycarbonate without seriously compromising the properties of the resin under normal molding conditions.